Species Trans Research Articles

Platinum(II), palladium(II) and rhodium(I) complexes of o-, m- and p-Ph2PC6H4PO(OEt)2. PtCl2–SnCl2 Hydroformylation catalysts modified with phosphonated triarylphosphines

An improved route to the bulky phosphine o-Ph2PC6H4PO(OEt)2o-1 has been elaborated. The isomers [PtCl2L2], L = o- (2), m- (3) or p-1 (4), were made by treatment of [PtCl2(cod)] with the appropriate phosphine. Complex 2 has a trans configuration whereas the m and p isomers, 3 and 4 are cis, reflecting the greater bulk of the o isomer. Crystal structure analyses of o-1 and its platinum complex 2 indicated normal dimensions for the tertiary phosphine in both and the considerable asymmetric steric bulk of o-1. Abstraction of the chloro ligands in 2 occurs upon addition of AgSbF6 and the resulting dicationic bis P,O-chelate 5 has a cis geometry. The palladium complexes [PdCl2L2], L = o- (6), m- (7), or p-1 (8) were made by treatment of [PdCl2(NCPh)2] with the appropriate phosphine but, in contrast to the platinum analogues, the o isomer 6 has a cis configuration and the m and p isomers 7 and 8 are predominantly trans. Complex 6 is fluxional: variable temperature 31P NMR spectroscopy is consistent with hemilabile behaviour of the ligand with reversible co-ordination of the PO of the phosphonate functionality. Treatment of [Rh2Cl2(CO)4] with o-1 gave the mononuclear chelate [RhCl(CO)(o-1)] (9) which upon addition of further o-1 gave predominantly the fluxional species trans-[RhCl(CO)(o-1)2]. The platinum complexes 2, 3 and 4 when combined with SnCl2 catalyse the hydroformylation of but-2-ene and but-1-ene.

Gold(III) derivatives with C(4)-aurated 1-phenylpyrazole

The reaction of 1-phenylpyrazole (HL), with gold(III) chloride has been studied. Besides a 1:1 adduct [Au(HL)Cl 3] 1, where the ligand is bonded through the nitrogen atom, several C(4) aurated species have been isolated. Thus treatment of [AuCl 3] 2 with HL in dichloromethane solution affords a complex, [Au(L)Cl 2 .HCl] n , 2, where the gold atom is bonded to the 4-carbon atom of the pyrazole ligand. Deprotonation of complex 2 by means of the not coordinating base 1,8-bis(dimethylamino)naphthalene (proton sponge), B, affords the salt [BH][Au(L)Cl 3], 3, whereas reaction of 2 with 3,5-Me 2py and PPh 3 (molar ratio 1:2) gives the neutral species trans-[Au(L)(3,5-Me 2py)Cl 2], 4, and cis-[Au(L)(PPh 3)Cl 2], 5, respectively. The structure of compound 4 solved by X-ray diffraction, unambiguously shows the anionic ligand L bonded to the gold ion through the C4 atom. Alternatively, compounds 4 and 5 can be obtained in two steps, i.e. deprotonation of 2 with NaOH to give [Au(L)Cl 2] n , 6, and reaction of 6 with 3,5-Me 2py and PPh 3, respectively. The new species were characterized by elemental analyses, conductivity measurements, IR, NMR and FAB-MS spectroscopy.

Reactions of platinum(II)-alkyne and -alkynyl complexes with the hydroxy compounds HO(CH 2) 2X(X = Br, I, OH)

The cationic solvento species trans-[Pt(Me)(PPh 3) 2(solv)][BF 4] (solv = CH 2Cl 2, Et 2O) reacts with 1.5 equiv. of p-tolylacetylene in the presence of a 10-fold excess of the hydroxylated compounds HOCH 2CH 2X (X = Br, I, OH) to give the corresponding (alkoxy)alkyl carbene complexes trans-[Pt(Me)=C(OCH 2CH 2X)CH 2( p-tolyl)(PPh 3) 2][BF 4 ( 1–3). Complexes 1–3 were also obtained by reaction of the acetylide complex trans-[Pt(Me)(CCR)(PPh 3) 2] (R = p-tolyl) in the presence of 1 equiv. of HBF 4 with an excess of HOCH 2CH 2X. The carbene complex trans-[Pt(Me)=C(OCH 2CH 2Cl)CH 2R(PPh 3) 2][BF 4] (R = p-tolyl) can be readily deprotonated by NEt 3 to afford the vinyl complex trans-[Pt(Me)C(OCH 2CH 2Cl)CH(R)(PPh 3) 2] ( 4). A similar behavior is observed also for 1–3 when treated with a base.

Theoretical Studies on the Photochemistry of the Cis-to-Trans Conversion in Dinuclear Gold Halide Bis(diphenylphosphino)ethylene Complexes

Ab initio calculations were carried out on cis- and trans-(diphosphino)ethylene digold halide, Au2X2C2H2(PH2)2 (X = Cl, Br, I), the model compounds for dinuclear gold(I) bis(diphenylphosphino)ethylene complexes, Au2X2(dppee). The calculations reveal aurophilic interactions in the cis compound, thus stabilizing the cis complex with respect to the trans species. The aurophilic interaction, caused by an interplay between relativistic and electron correlation effects, increases with increasing softness of the ligand attached to gold. Excited-state calculations show ethylene π* contributions only for the cis compound, but not for the trans compound, thus explaining why the trans complex does not isomerize to the cis compound upon UV radiation at wavelengths greater than 220 nm. The singlet excitation can be best described as a charge-transfer transition from the halogen lone pair to the Au (5d6s6p) orbitals with strong intermixing from phosphorus (sp) orbitals. Because of symmetry reasons, these orbitals mix w...

Monofunctional trans-Pt II(NH 3) 2 modification of pyrimidine-rich deoxyoligonucleotides: direct platination and use of a protective group

Ways are studied to obtain pyrimidine-rich deoxyoligonucleotides (ON) ( n=4−8) which are monofunctionally modified with a trans-[Pt(NH 3) 2Cl] + entity: (i) direct platination of the ON with trans-Pt(NH 3) 2Cl 2; (ii) platination with the monoaqua species trans-[Pt(NH 3) 2Cl(H 2O)] +; (iii) platination with trans-Pt(NH 3) 2(1-MeT)Cl or trans-[Pt(NH 3) 2(1-MeT)(H 2O] + containing the acid-labile protective group 1-MeT (1-MeT=1-methylthymine anion). Reactions with the oligonucleotides are followed by 1H NMR spectroscopy and HPLC and the products are characterized by ESI MS and 1H NMR. It was the aim of this work to find ways of preparing monofunctionally ( trans-Pt II(NH 3) 2) modified ON on a large scale for potential application in the antisense technology.

Interspecific variation in floral fragrances within the genus Narcissus (Amaryllidaceae)

To improve our understanding of the floral biology, pollination, and systematics of the genus Narcissus, a comparative study was made of flower volatiles from nine species native to southern Spain using headspace collection and GC-MS analysis. The species fell into three fragrance types based on the identity o! their major volatiles. In all but one species the fragrances consisted mainly of monoterpene isoprenoids mixed with benzenoids: in six species trans-~-ocimene occurred in high proportions, in two others it was lacking; the last species had a fragrance dominated by fatty acid derivatives, mixed with terpenoids. Two of the species showed marked intraspecific variation in many of their volatiles. When the volatile data matrix of all species was subjected to cluster analyses and the resulting phenetic trees compared with currently recognized taxo- nomic groups, there was no congruence at the subgeneric level. However, there was considerable agreement at the sectional level, although in most sections we studied only a single species. This apparent agreement was stronger when the volatiles were analyzed according to shared biosynthetic pathways rather than treated individually, pointing to the higher value of using biosynthetic pathways for uncovering and confirming phe- netic, and probable evolutionary, relationships among species. In terms of possible selective pressures from pollinators in shaping fragrance chemistry, available information on the pollination of our species suggested an association between fragrance and types of pollinators. Two pollinator-fragrance groups were apparent: (1) species pollinated by insects that include butterflies and moths displayed fragrances containing volatiles typical of moth-pollinated flowers, most particularly indole combined with high amounts of esters, and (21 species visited exclusively by insects other than butterflies and moths, especially by bees and flies, had fra- grances lacking this combination of volatiles. Narcissus assoanus was unusual among our species in having both fragrance chemotypes. Future pollination studies of Narcissus in the field are needed to test the reliability and predictability of the proposed fragrance-pollinator associations. © 1997 Elsevier Science Ltd

Platinum amides from platinum nitriles: X-ray crystal structure of trans-dichloro-bis(1-imino-1-hydroxy-2,2-dimethylpropane)platinum(II)

The bisamide complex trans-[PtCl 2HN=C(OH)Bu t 2] ( 1) has been prepared by hydrolysis of dichlorobis(tertiary-butylnitrile)-platinum(II) and characterized via single crystal X-ray diffraction. The complex crystallizes in the Pbcn (No. 60) space group with the cell parameters a = 11,.692(2), b = 22.214(3) and c = 18.515(2) A ̊ . Twelve complex molecules are present in the cell where triplets of the are stabilized by intermolecular hydrogen bonds involving N, Cl and O atoms. The structure has a strict similarity with that previously reported (D.B. Brown, R.D. Burbank and M.B. Robin, J. Am. Chem. Soc., 91 (1969) 2895) (the refinement, however, showed all the non-H atoms and converged to R = 0.0471 for 1003 observed reflections ( F b > 6 σ( F e)) in the present work, whereas the structure analysis of the previous work did not show most of the atoms of a molecule in the asymmetric unit and the refinement converged to R = 0.107 for 2047 observed reflections) and proposed to contain, besides the yellow bisamide ( 1 ∼ 70%), also a second yellow material ( II. ∼ 20%) and a third blue material ( III. ∼ 10%). The latter two had an analytical composition similar to that of the first one and were formulated as isomeric dichlorobis(amidato)platinum(IV) species. The mixed amidenitrile species trans-[PtCl 2[HN=C(OH)Bu t)(NCBu t)] ( 2 has also been characterized. It has NMR signals coincident with those of compound II, its space group and cell parameters are very close to those of 1, and it has a tendency to cocrystallize with 1 in the molar ratio 2:1 in favor of 2. The geometry of the amide ligands in the enol tautomeric form appears to be ideal for favoring the face-to-face association of platinum units stabilized by interfacial hydrogen bonds. In the case of cis geometry (corresponding cis isomer of 1), platinum dimers with an intermetallic distance of 3.165(1) Å were formed: in contrast, in the case of trans geometry (compound 1 presently investigated) platinum triplets with an intermetallic distance of 3.668(1) Å were established. In both cases the preferred conformation is staggered and the shortest distance between platinum atoms in different dimers ( cis isomer) or triplets ( trans isomer) is in excess of 4.17 Å. Therefore, a special role of the coordination geometry appears to be in determining the mode of association of platinum monomers in oligomers.

W 2Cl 4(NR 2) 2(PR 3′) 2 molecules—9. New mixed valent W III/W IV face-sharing bioctahedral complexes with chelating bis(diphenylphosphino)propane and dialkylamido ligands

The triply-bonded ditungsten(III) species trans, trans-W 2Cl 4(NBu 2 n ) 2(dppp) ( 1) and a new mixed-valent W III/W IV complex (dppp)ClW( μ-Cl) 3WCl 2(NBu 2 n ) ( 3) have been isolated from the reaction of W 2Cl 4(NBu 2 n ) 2(NHBu 2 n ) 2 with 1,3-bis(diphenylphosphino)propane (dppp). A complex similar to 3, (dppp)ClW(μ-Cl) 3WCl 2(NEt 2) ( 2), has also been prepared. Both 2 and 3 are characterized by a W 2 7+ core and they adopt face-sharing bioctahedral geometry with a chelating dppp ligand. The WW distances in 2 and 3 are both 2.660(1) Å and each of them shows an EPR signal at g = 1.88. The structure of 1 contains a W 2 6+ core with a WW distance of 2.3055(8) Å. It has a bridging dppp ligand and a trans,trans stereochemistry.

High Nuclearity Heterometallic Gold(I)-Containing Derivatives from Manganese(I) and Ruthenium(II) dppm Complexes via Diphosphinomethanide Intermediates

The cationic complexes trans-[RuCl(L)(dppm)2]+ (1a, L = CO; 1b, L = CNtBu; 1c, L = CNPh), trans-[Ru(CNR)2(dppm)2]2+ (1d, R = tBu; 1e, R = Ph), and trans-[Mn(CO)2(dppm)2]+ (1f) are selectively deprotonated with KOH or NaMeO affording the mixed ligand dppm/dppm-H complexes (dppm-H = [(PPh2)2CH]-) trans-[RuCl(L)(dppm)(dppm-H)] (2a−c), trans-[Ru(CNR)2(dppm)(dppm-H)]+ (2d,e), and trans-[Mn(CO)2(dppm)(dppm-H)] (2f), respectively. Under more forcing conditions, 2d and 2e undergo a second deprotonation reaction to give trans-[Ru(CNR)2(dppm-H)2] (3d,e). The treatment of 1f with [AuCl(PPh3)] in the adequate stoichiometric ratio, in the presence of an excess of KOH, affords the heterometallic complexes trans-[Mn(CO)2(dppm){(PPh2)2CH(AuPPh3)}]+ (4f), trans-[Mn(CO)2{(PPh2)2CH(AuPPh3)}2]+ (5f), trans-[Mn(CO)2{(PPh2)2CH(AuPPh3)}{(PPh2)2C(AuPPh3)2}]+ (6f), and trans-[Mn(CO)2{(PPh2)2C(AuPPh3)2}2]+ (7f) as a result of the stepwise double metalation of the two dppm ligands. 4f is more conveniently prepared by reaction of 2f with an excess of [AuCl(PPh3)], although a good purification of the complex is not achieved. For 5f, two isomers are present, in the same proportion, corresponding to the mutually syn or anti disposition of the two Au(PPh3) fragments. By contrast, in the treatment of the ruthenium derivatives 1d and 1e with [AuCl(PPh3)] in the presence of KOH, the products of partial metalation of the dppm ligands were not obtained and only the fully metalated pentametallic species trans-[Ru(CNR)2{(PPh2)2C(AuPPh3)2}2]2+ (7d and 7e) were isolated. For 2a and 7e, an X-ray diffraction study was undertaken.

Synthetic, structural and inelastic neutron scattering studies of the hydridobridged cationic complexes [(PMe 3) 2(Y) Pt(μ-H)Pt(Y)(PMe 3) 2] + (Y = Ph, C 6F 5, C 6Cl 5) and of [(PEt 3) 2(H)Pt(μ-H) Pt(Ph) (PEt 3) 2] +

The mono-hydrido-bridgeddiplatinumcomplexes [(PMe 3) 2(C 6X 5)Pt(μ-H)Pt(C 6X 5)(PMe 3) 2](CF 3SO 3) (X = H, F, Cl) were prepared from the corresponding mononuclear species trans- [PtH(C 6X 5)(PMe 3) 2] and trans-[Pt(C 6X 5)(S)(PMe 3) 2](CF 3SO 3) (S-weakly coadinating solvent). The X-ray crystal structures of [(PMe 3) 2(Ph)Pt(μ-H)Pt(Ph)(PMe 3) 2] [BPh 4], prepared from the cares triflate (space group P 1, a=13.731(5), b=16.192(2), c=23.425(8) A ̊ , α=96.46(2), β=100.54(3), y=95.05(2)°, Z=4, R=0.043, R w =0.056 for 6914 observed reflections) and of [(PMe 3) 2(C 6F 5)Pt(μ-H)Pt(C 6F 5)(PMe 3) 2](CF 3SO 3)-CH 2Cl 2 (space group P2 1/ n, a=11.762(2), b=19.500(3), c=19.112(3), β=105.64(1), Z=4, R=0.038, R W=0.049 for 2528 observed reflections) were determined. Both cations contain the two planar (Pt(C 6X 5) (PMe 3) 2) moieties bridged by a hydride ligand, the Pt-Pt bonds being 3.0641(7) and 3.0969(9) Å for X = H and 3.009(1) Å for X = F. Inelastic incoherent neutron scattering studies were carried out on [(PMe 3) 2(C 6)F 5)Pt(μ-H)-Pt(C 6F 5)(PMe 3) 2](CF 3SO 3), ( PEt 3) 2( H) Pt( μ- H) Pt( Ph)( PEt 3) 2]( CF 3 SO 3) and [( PEt 3) 2( Ph) Pt( μ- H) Pt( Ph)( PEt 3) 2]( CF 3 SO 3), and vibrational data for the PtHPt fragments obtained. The values of the ν asynm/ ν sym ratios and a semi-empirical correlation were used to obtain approximate values of the Pt-H-Pt bond angles in compounds of this type.

One-pot synthesis, physicochemical characterization and crystal structures of cis- and trans-(1,4,8,11-tetraazacyclotetradecane)-dichloroiron(III) complexes †

The synthesis and characterization of cis- and trans-[Fe(cyclam)Cl2]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) are described. The assignment of geometrical configuration to these complexes has been made on the basis of their infrared spectra in the 800–900 cm–1 region. In addition, the molecular structures of the cis and trans derivatives were determined by X-ray diffraction. Both complexes have a d5 electronic system, the cis and trans species being respectively in a high spin and a low spin configuration. These two isomers are fully characterized by electrochemistry and they are simultaneously observed in the reaction mixture by cyclic voltammetry. This study shows that the reactivity towards dioxygen of the two reduced isomers is different, and that the formation of the oxygenated species is not observed in some solvents.

Synthesis, Molecular Structures, and Fluxional Behavior of dppm-Bridged Complexes of Platinum(II) with Linear Gold(I), Trigonal Silver(I), or Tetrahedral Mercury(II) Centers

The complexes [PtR(dppm-P,P)(dppm-P)]PF6 (R = Me, Et, Ph) react with [AuCl(SMe2)] to generate the dppm-bridged platinum−gold complexes trans-[PtClR(μ-dppm)2Au]PF6 (1). Addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of silver(I) acetate, followed by acetyl chloride, yields the neutral platinum-silver species trans-[PtClR(μ-dppm)2AgCl] (2). Similarly, addition of [PtR(dppm-P,P)(dppm-P)]Cl to a solution of mercury(II) acetate, followed by acetyl chloride, yields the neutral platinum-mercury species trans-[PtClR(μ-dppm)2HgCl2] (3). Each of the complexes has been characterized by 1H and 31P{1H} NMR spectroscopy and by elemental analysis. The crystal structure of 1 as its methyl derivative 1a (CHCl3 solvate) has been determined by X-ray diffraction. The compound exhibits approximate square-planar geometry at platinum and linear geometry at gold. The platinum−gold internuclear distance is 3.008(1) A. The methyl complex 2a crystallizes as its CHCl3 solvate. The geometry at platinum is distorted square planar...

Ligand Structural Effects on the Electrochemistry of Chromium(III) Amino Carboxylate Complexes.

The aqueous electrochemical behavior of 10 Cr(III) complexes with potentially tri- and hexadentate amino carboxylate ligands is reported and is shown to depend on the composition and spatial arrangement of the donor atom set. Complexes with two amine and four carboxylate donors (N(2)O(4)) and two amine, one aquo, and three carboxylate donors (N(2)O(3)O') in which the N atoms are coordinated cis to one another undergo chemically and electrochemically reversible reduction at ca. -1.4 and ca. -1.2 V vs SCE, respectively. However, complexes with a trans-N(2)O(4) donor atom set, as exemplified by Cr(MIDA)(2)(-) (MIDA(2)(-) = N-methyliminodiacetate), undergo quasi-reversible Cr(III/II) reduction at ca. -1.4 V that is followed by a sequence of reactions which establishes an electrochemical square scheme. The chemical reactions in the scheme involve displacement of a bound carboxylate group following reduction to Cr(II) and its reattachment after reoxidation to Cr(III). This mechanistic sequence is analyzed by digital simulation, and values of formal potentials, transfer coefficients, and chemical and electrochemical rate constants are reported for Cr(MIDA)(2)(-) and its N-ethyl homolog. The difference in electrochemical behavior between cis- and trans-N(2)O(4) complexes is attributed to differences in the Jahn-Teller distortions experienced by these structures upon reduction to Cr(II). It is proposed that simultaneous N-Cr-N bond elongation, which is possible only for trans species, leads to greater strain in the facially coordinated N-alkyliminodiacetate ligand and thus increases the barrier to electron transfer and facilitates Cr-carboxylate bond cleavage after reduction.

Non-isothermal spectrophotometric kinetics applied to inorganic reactions

Kinetic constants and activation parameters of some inorganic reactions in solution have been obtained very easily and with great accuracy from variable temperature spectrophotometric kinetic data using a method based on non-isothermal analysis. The reactions studied under various experimental conditions to test the method were the cis-trans isomerization of the cation [Pt(PEt 3) 2(CH 3)(C 2H 5OH)] + in ethanol and the thermal decomposition of the alkyl solvent species trans-[Pt(PEt 3) 2(n-C 4H 9)(CH 3OH)] + to yield the trans-hydride [Pt(PEt 3) 2(H)(CH 3OH)] + in methanol. The results are compared with those obtained by the traditional isothermal method. A suitable experimental apparatus and software is described for routine measurements.

Alkoxides as ancillary ligands in organolanthanide chemistry: Synthesis, reactivity, α-olefin and diene polymerization by [Y(C 5Me 5)(OC 6H t3Bu 2)(μ-H)] 2

Terminal olefins H 2CCHR (R=H, Me, n-Bu) react regiospecifically and irreversibly with μ-H dimer [Y(C 5Me 5)(OAr)(μ-H)] 2 ( 1) to give the μ- n-alkyl species trans-[Y(C 5Me 5)(OAr)] 2(μ-H)(μ-CH 2CH 2R) (R=H ( 2), Me ( 3), n-Bu ( 4)) respectively. Reaction of[Y(C 5Me 5)(OAr)(μ-D)] 2 ( 4-D) (prepared from (C 5Me 5)Y(OAr)CH(SiMe 3) 2 and D 2) with propene yields selectively only trans-[Y(C 5Me 5)(OAr)] 2(μ-D)(μ-CH 2CHDMe) ( 4-D), confirming the non-reversibility of olefin insertion. Compounds 1–4 polymerize ethene and are single-component catalysts for the polymerization of α-olefins and non-conjugated dienes. Dissolution of 1 in neat 1-hexene (to give 4 in situ) results in slow polymerization to yield poly(1-hexene) with M w=15700, M w/ M n=1.67. 1 cyclopolymerizes neat 1,5-hexadiene to poly(methylene-1,3-cyclopentane), rather than cyclization to methylenecyclopentane.

Alkoxides as ancillary ligands in organolanthanide chemistry: synthesis of, reactivity of, and olefin polymerization by the .mu.-hydride-.mu.-alkyl compounds [Y(C5Me5)(OC6H3tBu2)]2(.mu.-H)(.mu.-alkyl)

Reaction of Y(C[sub 5]Me[sub 5])(OAr)[sub 2] (2; OAr = 0.2,6-C[sub 6]H[sub 3][sup t]Bu[sub 2]) with MCH(SiMe[sub 3])[sub 2] (M = Li, K) affords Y(C[sub 5]Me[sub 5])(OAr)[l brace]CH(SiMe[sub 3])[sub 2][r brace] (3), which on subsequent hydrogenation (20 bar, 25[degree]C) gives the [mu]-H dimer [YC[sub 5]Me[sub 5](OAr)([mu]-H)][sub 2] (4). Terminal olefins H[sub 2]C=CHR (R = H, Me, Et, n-Bu) react regiospecifically and irreversibly with 4 to give the [mu]-n-alkyl species trans-[Y(C[sub 5]Me[sub 5])(OAr)][sub 2]([mu]-H)([mu]-CH[sub 2] CH[sub 2]R) (R = H (5), Me (6), Et (7), n-Bu (8)), respectively. Reaction of [Y(C[sub 5]Me[sub 5])(OAr)([mu]-D)][sub 2] (4-D) (prepared from 3 and D[sub 2]) with propene yields selectively only trans-[Y(C[sub 5]Me[sub 5])(OAr)][sub 2]([mu]-D)([mu]-CH[sub 2]C HDMe) (6-D), confirming the nonreversibility of olefin insertion. Compounds 4-8 polymerize ethene and are single-component catalysts for the polymerization of [alpha]-olefins and nonconjugated dienes. Dissolution of 4 in neat 1-hexene (to give 8 in situ) results in slow polymerization to yield poly(1-hexene) with M[sub w] = 15 700 and M[sub w]/M[sub n] = 1.67. 4 cyclopolymerizes neat 1,5-hexadiene to poly(methylene-1,3-cyclopentanediyl) rather than promotes cyclization to methylenecyclopentane. The [mu]-alkyls 5-8 show diastereotopic [alpha]-CH[sub 3] resonances, implying idealized C[sub 2], rather than C[sub 2v] geometry, which indicates a mutually trans geometry for themore » attendant C[sub 5]Me[sub 5] and OAr ligands. In 6, exchange of the two diastereotopic C[sub [alpha]]H[sub 2] hydrogens by inversion at Y([mu]-C[sub 5])Y occurs with [Delta]G* = 11.1 [+-] 0.5 kcal mol[sup [minus]1] ([minus]25[degree]C), and tert-butyl group equilibation on the same phenoxide occurs with [Delta]G* = 9.0 [+-] 0.5 kcal mol[sup [minus]1] ([minus]93[degree]C). 60 refs., 1 fig., 2 tabs.« less

Linear polyesters of diethylene glycol with cis- and trans-4-cyclohexene-1,2-dicarboxylic acid. Synthesis, characterization and NMR structural study

Two linear polyesters from cis- and trans-cyclohexene-1,2-dicarboxylic acid and diethylene glycol have been synthesized by solution polycondensation in m-xylene. Fractions of the two polyesters of M n ca 10,000 g/mol were used for identification and structural studies, along with cis- and trans-4-cyclohexene-1,2-dicarboxydiethyl ester, used as models. Thermal and i.r. spectral data of models and polymers are reported. The structures of the cis and trans species could be unambiguously elucidated by means of 1H- and 13C-NMR.

Kinetic study of .beta.-hydride elimination from monoalkyl solvento complexes of platinum(II)

Electrophilic attack by a proton on cis-[Pt(PEt 3 ) 2 (R) 2 ] (R=C 2 H 5 , C 2 D 5 , n-C 3 H 7 , n-C 4 H 9 ) complexes in protic solvents and subsequent fast isomerization of the cis-alkyl(solvento) intermediates produce the solvento species trans-[Pt(PEt 3 ) 2 (R)(S)]+(S=solvent). These latter undergo a facile thermal decomposition, yielding trans-[Pt(PEt 3 ) 2 (H)(S)] + and olefins under very mild conditions. The kinetics were followed by means of a variety of experimental techniques, including 1 H and 31 P NMR, GLC, and conventional spectrophotometry

Synthesis, characterization and crystal structure of oxobis( p-thiocresolato)terpyridinerhenium(V), a new cationic, six-coordinate thiolato complex of rhenium

The new six-coordinate rhenium(V) complex, oxobis( p-thiocresolato)terpyridinerhenium(V), was synthesized from [ReO 2(py) 4]CF 3SO 3 and characterized by elemental analysis, thin-layer chromatography, FAB mass spectroscopy, IR and 1H NMR of the perrhenate salt, as well as by a single crystal X-ray structure determination of the hexafluorophosphate salt. This characterization establishes the structure of the complex in both solid state and solution to be the symmetrical mer(N,N,N),trans(S,S) species in which the central N atom of the terpyridine ligand is situated trans to the ReO linkage. The X-ray and NMR studies demonstrate that the solution and solid state structures are identical.

The cis- and trans-effects of cyanide in substitution at platinum(II)

The cis- and trans-[Pt(am)2Cl2] isomers (am = dimethylamine, pyridine, 4-cyanopyridine, 4-chloropyridine, 2-methylpyridine, 4-methylpyridine, 2,4-dimethylpyridine, 4-ethylpyridine, morpholine or piperidine), react rapidly with excess CN– in methanol to form the corresponding cis- and trans-[Pt(am)2(CN)2] species which then react further to give [Pt(CN)4]2–. The kinetics of the slow step, [Pt(am)2(CN)2]+ CN–→[Pt(am)(CN)3]–+ am, has been studied. In spite of the strong trans effect of CN– the trans species are all more reactive than the corresponding cis isomers. The second-order rate constants are sensitive to the nature of am; plots of log k2 against the pKa of Ham+ are linear but the slope for the trans isomers (–0.27) is much greater than that for the cis isomers (–0.07). The rate constants for the displacement of o-methyl substituted pyridines are smaller than predicted from their basicity. This steric hindrance effect is much more marked in the trans isomers. The complexes with am = NH3 and NH2Me are similarly less reactive than might be predicted but the effect is the same in both isomers. The results are explained in terms of the trans effect of cyanide and its effect upon the intrinsic reactivities and nucleophilic discriminations of the substrates.